This section is intended to introduce the reader to various aspects of art, which may be related to various aspects of the present invention that are described and/or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of the various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.
Radio-frequency identification (RFID) uses an object, an RFID tag (hereinafter “tag”), which interacts with transmitted radio waves, for example in systems for theft prevention, supply chain management or access to buildings. A typical tag comprises at least two parts: an antenna that receives and transmits a radio-frequency (RF) signal, and an integrated circuit that stores and processes information and processes the signal. Some tags, called “active”, comprise a battery and are thus autonomous, while “passive” tags have no battery and therefore have to rely on external power, often the received RF signal, in order to function properly.
U.S. 2008/0307884 describes a non-contact shock sensor, which may be used to detect if an object has been submitted to shocks during transport. The sensor comprises a RFID chip, a conductor loop and a movable mass. When submitted to sufficient acceleration, the mass breaks the loop, which can thereafter be read out via the RFID chip.
U.S. 2009/0299570 describes a tire module for making tire measurements that, presumably, are sent to a processor in the vehicle on which the tire is mounted. In order to reduce the load on a battery, it is proposed to activate the module only when the tire has reached a predetermined velocity.
It has also been proposed, for example in WO 2006032613 and U.S. Pat. No. 6,357,005, to use tags on or in digital supports such as CDs and DVDs. This may for example be done in order to protect the content on the digital support (information necessary to access the content is comprised in the tag) or to store preferences regarding the playback of the content.
While this works well in most cases, there may be problems if there are more than one tag within range of the reader. This may for example be the case when a user puts DVDs on the DVD player, since the tags on these DVDs may be as close as the one in the player. One problem with this, in particular for passive tags, is that the signal power emitted by the reader has to be shared, which may lead to decreased communication quality. A further problem is that it may be difficult for the reader to know exactly which response to take account of. For example, if one DVD returns that it should be played at volume 7 and another DVD requires volume 16, the reader would not know which volume value to choose.
It can therefore be appreciated that there is a need for a solution that overcomes these problems and allows a reader to interact with the present tag without disturbance from other tags.
An obvious solution to this problem would be to shield the readers, but the present invention provides a different, surprising solution to the problem, as will be seen in the description of the preferred embodiments hereinafter.